With LCDs being applied to more and more fields, one emerging trend has been for LCDs to become larger in size. A large size LCD provides a bigger viewing area and high definition. LCDs employing thin film transistors (TFTs) are called TFT-LCDs. Generally, TFT-LCDs have a problem of gate delay due to the long gate lines therein. This problem is also known as gate delay phenomenon of scanning signals. Gate delay typically results in image flickering or other malfunction or poor performance. In a large size LCD with very long gate lines, gate delay may be a serious problem.
Referring to FIG. 3, a related art LCD 100 includes a gate driving circuit 110, a data driving circuit 120, and a liquid crystal panel 130. The gate driving circuit 110 is configured for providing a plurality of scanning signals to the liquid crystal panel 130, and the data driving circuit 120 is configured for providing a plurality of gray scale voltages to the liquid crystal panel 130.
The liquid crystal panel 130 includes a plurality of gate lines 101 which are parallel to each other, a plurality of data lines 102 which are parallel to each other and intersect the gate lines 101, a plurality of TFTs 103 arranged at crossings of the gate lines 101 and the data lines 102, a plurality of pixel electrodes 104, and a plurality of common electrodes 105 opposite to the pixel electrodes 104. A minimum area bounded by two adjacent gate lines 101 and two adjacent data lines 102 is defined as a pixel area. The gate driving circuit 110 outputs a plurality of scanning signals in sequence to the gate lines 101. The data driving circuit 120 applies a plurality of gray scale voltages to source electrodes of corresponding TFTs 103 when each gate line 101 is scanned.
Referring also to FIG. 4, an equivalent circuit diagram of a pixel area is shown. A gate electrode 1031 of the TFT 103 is connected to the corresponding gate line 101, a source electrode 1032 of the TFT 103 is connected to the corresponding data line 102, and a drain electrode 1033 of the TFT 103 is connected to a corresponding pixel electrode 104. Because the gate line 101 has a certain resistance R itself, and a parasitic capacitance Cgd is generated between the gate electrode 1031 and the drain electrode 1033, thereby forming a so-called resistance-capacitance (RC) delay circuit. In one gate line 101, therefore, many such RC delay circuits are connected in series. The RC delay circuit can delay the scanning signal applied to the gate line 101, and thus the waveform of the scanning signal can be distorted.
Referring also to FIG. 5, this shows two waveforms of a scanning signal waveforms provided at two ends of one gate line 101. One of the ends is adjacent to the gate driving circuit 110, and the other end is far away from the gate driving circuit 110. “Vg1” denotes the waveform of the scanning signal that is at the end adjacent to the gate driving circuit 110, and “Vg2” denotes the waveform of the scanning signal that is at the end far away from the gate driving circuit 110. That is, the waveform “Vg2” represents the distorted waveform of the scanning signal that is delayed by the serial RC delay circuits. “Von” denotes a turn-on voltage of each TFT 103, and “Voff” denotes a turn-off voltage of each TFT 103. Because of the distortions of the waveform of the scanning signal, turning on of a TFT 103 far away from the gate driving circuit 110 is delayed. For example, the turning on may be delayed “t” seconds. That is, an actual on-state period of the TFTs 103 far away from the gate driving circuit 110 is shorter than it is supposed to be.
Because a gray scale voltage will not be applied to the drain electrode of any TFT 103 until the TFT 103 is turned on, the TFTs 103 which are far away from the gate driving circuit 110 lack charging of the gray scale voltage. Thus, the image display in the corresponding pixel area is deteriorated. Commonly, many pixel areas are affected because the corresponding TFTs 103 lack charging of gray scale voltages. In this case, the image of the LCD 100 has flickering.
What is needed, therefore, is a liquid crystal display which can overcome the above-described deficiencies.